I found him laying on the bottom of his tank when I did my nightly "play with the fishies"

I thought he was just asleep, but I wiggled my finger in his water and didn't move. Then I got Ivy in her cup and put her cup floating in his tank to see if he would "wake up". Nothing. He IS alive, but not doing too well. He looks terrible. I quickly did a 100% WC, added more salt, stuck an air stone in there (on low, but it'll put more oxygen in the water) and a teensy bit of maracyn (incase it's something bacterial). Also covered his tank with a dark cloth to calm him down. I can't think of anything that would have contaminated his water.... I'm really worried about my boy.

He's in a 2 gallon tank with a 25W heater and two caves and a big bushy silk plant. Water temp is 75 degrees. He is almost acting as if he has SBD, AKA laying on the bottom, won't eat, and his body is kinda curved.